Technical Field
The present disclosure relates to a technique for identifying a target which is present in the vicinity of a vehicle.
Background Art
On-vehicle radar apparatuses have been used to transmit and receive a radar wave to detect information relating to a target (distance, relative speed, azimuth, and the like relative to the target) that has reflected the radar wave. For example, an on-vehicle radar apparatus is disclosed in JP-A-2011-017634. According to the disclosure well known, when a target is detected over a plurality of measurement cycles, the apparatus estimates the height of the target from the road surface, on the basis of the distribution (generation pattern of null points) of the received power.
In a generation pattern of null points, usually, the generation interval of null points becomes larger as the height from the road surface becomes smaller. In the case of a road surface object made of metal, such as a manhole, embedded in the road surface (hereinafter also referred to as low-level target), no null point is generated. However, as shown in FIGS. 10A and 10B, when a vehicle traveling a downward slope detects a low-level target on a horizontal road surface ahead of the vehicle, or when a vehicle traveling a horizontal road surface detects a low-level target set up on an upward slope ahead of the vehicle, the distribution of the received power is equivalent to that of a target having a height from the road surface (attention target that needs to be paid attention under the control such as of drive assist). In other words, in such a case, the low-level target is erroneously recognized as an attention target.
In contrast, whether a target is a low-level target or an attention target may be identified on the basis of the depth of the target determined from the distribution of reflection points, i.e. points that have reflected the radar wave. That is, a low-level target, such as a manhole, detected on an ordinary road is detected as an object having only a small depth since the size of the target in a depth direction as viewed from the vehicle is less than one meter at the most. On the other hand, other obstacles are also detected on a road, or particularly vehicles are detected as representatives of obstacles. In such a vehicle, the radar wave is reflected not only on the rear end surface of the vehicle, but also on an object inside the vehicle compartment after the radar wave's passing through the glass, or on the bottom surface of the vehicle body after the radar wave's reaching under the vehicle body. Therefore, the vehicle is detected as an object having a depth (see FIG. 4A). FIG. 4A is a result of fast Fourier transform of the reflected radar wave. The peak circled in the figure corresponds to a detected object.